The key driver of breathing rhythm is the preBötzinger Complex (preBötC) whose activity is modulated by various functional inputs, e.g., volitional, physiological, and emotional. While the preBötC is highly interconnected with other regions of the breathing central pattern generator (bCPG) in the brainstem, there is no data about the direct projections to either excitatory and inhibitory preBötC subpopulations from other elements of the bCPG or from suprapontine regions. Using modified rabies tracing, we identified neurons throughout the brain that send monosynaptic projections to identified excitatory and inhibitory preBötC neurons in mice. Within the brainstem, neurons from sites in the bCPG, including the contralateral preBötC, Bötzinger Complex, the nucleus of the solitary tract (NTS), parafacial region (pF
To understand visual functions mediated by intrinsically photosensitive melanopsin-expressing retinal ganglion cells (mRGCs), it is important to elucidate axonal projections from these cells into the brain. Initial studies reported that melanopsin is expressed only in retinal ganglion cells within the eye. However, recent studies in Opn4-Cre mice revealed Cre-mediated marker expression in multiple brain areas. These discoveries complicate the use of melanopsin-driven genetic labeling techniques to identify retinofugal projections specifically from mRGCs. To restrict labeling to mRGCs, we developed a recombinant adeno-associated virus (AAV) carrying a Cre-dependent reporter (human placental alkaline phosphatase) that was injected into the vitreous of Opn4-Cre mouse eyes. The labeling observed in the brain of these mice was necessarily restricted specifically to retinofugal projections from mRGCs in the injected eye. We found that mRGCs innervate multiple nuclei in the basal forebrain, hypothalamus, amygdala, thalamus and midbrain. Midline structures tended to be bilaterally innervated, whereas the lateral structures received mostly contralateral innervation. As validation of our approach, we found projection patterns largely corresponded with previously published results; however, we have also identified a few novel targets. Our discovery of projections to the central amygdala suggests a possible direct neural pathway for aversive responses to light in neonates. In addition, projections to the accessory optic system suggest that mRGCs play a direct role in visual tracking, responses that were previously attributed to other classes of retinal ganglion cells. Moreover, projections to the zona incerta raise the possibility that mRGCs could regulate visceral and sensory functions. However, additional studies are needed to investigate the actual photosensitivity of mRGCs that project to the different brain areas. Also, there is a concern of "overlabeling" with very sensitive reporters that uncover low levels of expression. Light-evoked signaling from these cells must be shown to be of sufficient sensitivity to elicit physiologically relevant responses.
Aromatase-expressing neuroendocrine neurons in the vertebrate male brain synthesize estradiol from circulating testosterone. This locally produced estradiol controls neural circuits underlying courtship vocalization, mating, aggression, and territory marking in male mice. How aromatase-expressing neuronal populations control these diverse estrogen-dependent male behaviors is poorly understood, and the function, if any, of aromatase-expressing neurons in females is unclear. Using targeted genetic approaches, we show that aromatase-expressing neurons within the male posterodorsal medial amygdala (MeApd) regulate components of aggression, but not other estrogen-dependent male-typical behaviors. Remarkably, aromatase-expressing MeApd neurons in females are specifically required for components of maternal aggression, which we show is distinct from intermale aggression in pattern and execution. Thus, aromatase-expressing MeApd neurons control distinct forms of aggression in the two sexes. Moreover, our findings indicate that complex social behaviors are separable in a modular manner at the level of genetically identified neuronal populations.
Aging results in cognitive decline and molecular changes that contribute to the risk of developing aging‐associated disease. As the aging population is rapidly increasing, with those over 60‐years‐old set to double by 2050, there is urgent need for a better understanding of the aging process and development of therapeutics for diseases of aging. Recent publications have shown that some aging‐associated phenotypes can be driven by plasma and plasma‐derived factors. In these studies, we sought to identify and validate detrimental effects of aged plasma and plasma‐derived factors on cognitive, histological, and molecular readouts in order to discover novel therapeutic targets for age‐related diseases. Our data show that administration of aged human plasma into young immunodeficient NSG (NOD.Cg‐Prkdcscid Il2rgtm1Wjl/SzJ) mice results in a decrease in neurogenesis and mild impairment in cognition. These results indicate that factors in aged human plasma can drive detrimental effects in the brains of young NSG mice. Plasma proteomics have identified aging signatures and specific proteins that are potential drivers of these negative effects in aging, and beta‐2 microglobulin (B2M) has been shown to be a pro‐aging factor with deleterious effects on cognition and neurogenesis. To confirm B2M as a negative factor, we treated young mice (WT; C57BL/6J) with recombinant human B2M and assessed changes in behavioral performance and histological markers. We found that systemic administration of B2M resulted in cognitive impairment during contextual fear conditioning and decreased neurogenesis, suggesting that it is a driver of negative effects during aging. Our data elucidate molecular pathways that contribute to the aging process and provide promising targets for developing translational therapeutics. Support or Funding Information Studies were funded by Alkahest.
Abstract Introduction Increasing age is the number one risk factor for developing cognitive decline and neurodegenerative disease. Aged humans and mice exhibit numerous molecular changes that contribute to a decline in cognitive function and increased risk of developing age‐associated diseases. Here, we characterize multiple age‐associated changes in male C57BL/6J mice to understand the translational utility of mouse aging. Methods Male C57BL/6J mice from various ages between 2 and 24 months of age were used to assess behavioral, as well as, histological and molecular changes across three modalities: neuronal, microgliosis/neuroinflammation, and the neurovascular unit (NVU). Additionally, a cohort of 4‐ and 22‐month‐old mice was used to assess blood‐brain barrier (BBB) breakdown. Mice in this cohort were treated with a high, acute dose of lipopolysaccharide (LPS, 10 mg/kg) or saline control 6 h prior to sacrifice followed by tail vein injection of 0.4 kDa sodium fluorescein (100 mg/kg) 2 h later. Results Aged mice showed a decline in cognitive and motor abilities alongside decreased neurogenesis, proliferation, and synapse density. Further, neuroinflammation and circulating proinflammatory cytokines were increased in aged mice. Additionally, we found changes at the BBB, including increased T cell infiltration in multiple brain regions and an exacerbation in BBB leakiness following chemical insult with age. There were also a number of readouts that were unchanged with age and have limited utility as markers of aging in male C57BL/6J mice. Conclusions Here we propose that these changes may be used as molecular and histological readouts that correspond to aging‐related behavioral decline. These comprehensive findings, in the context of the published literature, are an important resource toward deepening our understanding of normal aging and provide an important tool for studying aging in mice.
Author(s): Yang, Cindy | Advisor(s): Shah, Nirao M | Abstract: In many animals, the display of female sexual receptivity relies on internal states such as the hormonal status of the animal. Female mice, for example, are receptive toward males only peri-ovulation, presumably to maximize reproductive success. The sex hormone responsive neural circuits that regulate female receptivity remain largely unknown, but are likely sexually dimorphic since males do not become receptive under the same hormonal stimuli that induces ovulation and receptivity in females. Progesterone and the progesterone receptor (PR) are required for ovulation and female sexual receptivity. We have generated a genetically targeted PR reporter mouse to map a receptivity circuit. We find that PR is expressed in a sexually dimorphic pattern in many brain regions including a small pool of neurons in the ventromedial hypothalamus (VMH), a center required for receptive behavior. We find that PR-expressing neurons in the VMH send a female specific projection to the anteroventral periventricular nucleus (AVPV), a hypothalamic region that is critical for ovulation. These data suggest that a sexually dimorphic circuit mechanism coordinates ovulation and receptivity. With the genetic tools we have generated, we can now begin to probe the behavioral relevance of PR-expressing neurons.
Abstract A unique class of intrinsically photosensitive retinal ganglion cells in mammalian retinae has been recently discovered and characterized. These neurons can generate visual signals in the absence of inputs from rods and cones, the conventional photoreceptors in the visual system. These light sensitive ganglion cells (mRGCs) express the non-rod, non-cone photopigment melanopsin and play well documented roles in modulating pupil responses to light, photoentrainment of circadian rhythms, mood, sleep and other adaptive light functions. While most research efforts in mammals have focused on mRGCs in retina, recent studies reveal that melanopsin is expressed in non-retinal tissues. For example, light-evoked melanopsin activation in extra retinal tissue regulates pupil constriction in the iris and vasodilation in the vasculature of the heart and tail. As another example of nonretinal melanopsin expression we report here the previously unrecognized localization of this photopigment in nerve fibers within the cornea. Surprisingly, we were unable to detect light responses in the melanopsin-expressing corneal fibers in spite of our histological evidence based on genetically driven markers and antibody staining. We tested further for melanopsin localization in cell bodies of the trigeminal ganglia (TG), the principal nuclei of the peripheral nervous system that project sensory fibers to the cornea, and found expression of melanopsin mRNA in a subset of TG neurons. However, neither electrophysiological recordings nor calcium imaging revealed any light responsiveness in the melanopsin positive TG neurons. Given that we found no light-evoked activation of melanopsin-expressing fibers in cornea or in cell bodies in the TG, we propose that melanopsin protein might serve other sensory functions in the cornea. One justification for this idea is that melanopsin expressed in Drosophila photoreceptors can serve as a temperature sensor.
